Have you got your Facebook username yet? Probably not, unless you happen to be in the right time zone.

About an hour ago the site opened up its "vanity" addresses - the ability to register for a short Facebook web address that links directly to your profile page (I could pick facebook.com/bobbiejohnson, for example). Other social networking sites offer the same service, but Facebook is getting noticed because it has brought in after it's amassed more than 200 million users worldwide, not before. Charles looked at some of the questions raised by the landgrab already.

It's a strange exercise from a site that has always prided itself on getting people to use their real identities online, but perhaps the most confusing thing about the launch is its timing: 9pm Pacific time on a Friday night.

That makes it midnight on America's eastern seaboard, 5am in Britain and 6am in central Europe: not great if you live in any of those places. And how many Facebook users does that include? Well, it turns out, most of them.

The last reliable statistics I can see on Facebook's international makeup come from Ben Lorica at O'Reilly Radar, who suggested in March that around 33% of the site's user base is in Europe, with 39% in North America (the majority of whom are likely to live on the east coast).

That means, roughly, that just one third of Facebook's users live in a time zone where the username rush is happening during waking hours: and for the rest of us, only the most dedicated/insane Facebookers would consider getting up at the crack of dawn to ensure they registered their username.

In fact, the timing struck me as so odd that I put the question I put to Facebook earlier: if you want people to register their names, why do it so late and at the weekend?

Their response? That launching usernames at a low-traffic time was a way of managing demand, and to give users "as fair a shot as possible".

Certainly it's going to be more manageable if fewer people are doing it, but I'm not sure where fairness comes into it (unless "fair" means "giving our mates in Silicon Valley a chance to get there first").

It's also likely to encourage what a few internet wags are calling "facesquatting" - a brilliantly filthy double entendre coined by Anil Dash in his tremendously funny post on how the whole thing was going to play out. At the time of writing there don't seem to be many examples of facesquatting taking place (that link's NSFW), but surely it won't be long until somebody seriously gets taken for a ride.

In truth, though, I think the odd timing shows us something else: that the real target of Facebook usernames aren't users at all, but the companies, brands and high-profile celebrities who can be convinced to pay for services somewhere down the line.

Update: Facebook says 500,000 users grabbed their usernames within 15 minutes of the system going live, with no reports of major squabbles so far.

Commenters Sergio Montini and Liam Daly said they were awake during the wee small hours to make sure they got their preferred usernames; I spotted a handful of European Twitter users who took the same approach.